Bonobo mothers have been found to go that extra mile to help their sons procreate, according to a new study carried out in the Republic of Congo by an international team of researchers.

The study found that bonobo males who had their mothers living with them in their group were approximately three times more likely to have progeny than those whose mothers did not live with them. This appears to be the first study of mammals, other than humans, which investigates the effect of mothers’ presence on male fertility. The paper was published in Current Biology.

The study investigated two closely related groups of mammals – bonobos and chimpanzees – in both of which species the males are philopatric, or, show affinity to a particular place and return to it, and females tend to disperse. They observed 39 paternities from four groups in bonobos and 263 paternities from seven groups in chimps. When the females were living in the same group as their sons, the bonobos were 3.14 times more likely to sire offspring than when the mothers did not live with them. In chimpanzees, on the other hand, the males whose mothers lived with them were 1.26 times less likely to sire offspring.

Many of the 19 authors of the paper have contributed towards this problem in earlier work. They have observed that bonobo mothers actively encourage their sons to mate by taking them close to females who are mature and can have offspring; they stand in guard over the mating couple lest they be disturbed; they also interfere in mating attempts of other males, thereby decreasing their chances to mate and procreate!

Interesting and somewhat different patterns have been seen in other species, for example in orca – a large dolphin species which goes by the common name, killer whale – the mother leads the son to places where prey can be found easily. This increases their sons’ fitness to survive when compared with other males whose mothers did not live with them.

Studies on humans and orca revealed that such a behavioural pattern on the part of the mother actually increases her longevity and female post-reproductive lifespan. However, no such effect was observed in bonobos, who are not in captivity. This remains a subject for further study.